Speaker
Description
Background stars at cosmological distances that appear near the critical curves of galaxy clusters can be magnified by extreme factors of O(1000) and be detectable in deep observations with the Hubble or James Webb space telescopes. The stellar nature of this objects can be confirmed thanks to microlensing by stars in the galaxy cluster that can temporarily boost the flux of the lensed star by a factor of a few. Larger and more luminous objects, such as small star forming regions or globular clusters are virtually immune to microlensing so when microlensing is observed, it indirectly confirms the background object is as small as an individual star. The magnification experienced by these stars is also very sensitive to the presence of dark matter substructures. I will review a few examples where lensed stars have been used to set tight constraints on certain models of dark matter and discuss the prospects to get even tighter constraints from future observations.